This invention relates to a gas turbine engine and, more particularly, to a novel arrangement for the fan section thereof.
Considerable attention has been devoted to developing a gas turbine engine with the high specific thrust characteristics of a turbojet or low bypass turbofan at surpersonic speeds which can also be configured to exhibit the lower specific thrust, low noise, and low fuel consumption characteristic of a high bypass turbofan at subsonic speeds, in order that a mixed-mission aircraft may be developed. Such engines are generally referred to as variable cycle engines.
Several design approaches for a variable cycle engine have been developed. Thus, it has been proposed to increase the flow flexibility of a gas turbine engine by splitting the fan into two sections and providing a variable position duct intermediate the two sections, thereby to cause the flowpath between the forward and aft fan sections to be either in serial or parallel. While providing an increased margin of flow variability, engines of these types still lack sufficient flow flexibility to provide efficient operation over widely varying thrust levels and bypass ratios.
It has also been proposed to increase the flow modulation potential of a gas turbine engine by splitting the fan into two sections and placing each section in flow communication with a separate concentric bypass duct, each having a separate exhaust nozzle system. One problem associated with these and other prior art variable cycle engines of the split fan variety is the high cost and complexity resulting from utilization of multiple bypass ducts and exhaust nozzle systems.